531  
FXUS63 KARX 240915  
AFDARX  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE LA CROSSE WI  
315 AM CST TUE DEC 24 2024  
   
KEY MESSAGES  
 
- CLOUDY AND SEASONABLY MILD FOR MUCH OF THIS WEEK WITH HIGH TEMPERATURES  
IN THE 30S AND 40S, LOW TEMPERATURES FRIDAY THROUGH SUNDAY  
WILL BE WELL ABOVE NORMAL WITH MOST SPOTS NOT FALLING BELOW  
THE FREEZING MARK.  
 
- PRECIPITATION LIKELY (50-70% CHANCE) RETURNS BY LATE THURSDAY  
AND FRIDAY WITH RAIN BEING THE PREDOMINANT PRECIPITATION TYPE.  
ADDITIONAL PRECIPITATION CHANCES PERSIST THROUGH THE WEEKEND.  
 
 
   
DISCUSSION  
 
ISSUED AT 315 AM CST TUE DEC 24 2024  
 
TODAY - CHRISTMAS: CLOUDY WITH MILDER TEMPERATURES  
 
UPPER-LEVEL RIDGING AND SURFACE HIGH PRESSURE WILL BE THE NAME OF  
THE GAME FOR TODAY ALLOWING FOR FAIRLY LIGHT SURFACE WINDS  
THROUGHOUT THE DAY. HOWEVER, IN SPITE OF THE OVERALL SETUP, GUIDANCE  
CONTINUES TO SUGGEST HOLDING ONTO LOW-LEVEL MOISTURE THROUGHOUT THE  
DAY WHICH SHOULD KEEP THIS STRATUS DECK IN PLACE ACROSS MUCH OF THE  
REGION, ALBEIT A VERY THIN STRATUS. INTERESTING TO NOTE THE VAST  
DIFFERENCE IN THE 24.00Z GEFS AND EC FOR CLOUD COVER TODAY WHICH  
PAINTS VERY DIFFERENT PICTURES FOR CLEARING WITH THE GEFS FAVORING A  
VERY AGGRESSIVE SOLUTION FOR CLEARING OUT SKIES THIS AFTERNOON AS  
THE SURFACE HIGH MOVES DIRECTLY OVERHEAD. REGARDLESS, IF ANY SUN  
WERE TO PEAK THROUGH IT WOULD HAVE TO BE TODAY AS BOTH THE 24.00Z  
GEFS AND EC ENSEMBLE HAVE EVERY SINGLE MEMBER SHOWING 100% SKY COVER  
AFTER CHRISTMAS.  
 
AS FAR AS CHRISTMAS DAY IS CONCERNED, BEHIND THIS SUBTLE RIDGING A  
WEAK SHORTWAVE QUICKLY SWINGS THROUGH THE AREA WHICH COMBINED WITH  
THE LOW-LEVEL MOISTURE ALREADY IN PLACE MAY BE ENOUGH TO BRING SOME  
DRIZZLE TO PORTIONS OF THE AREA, PRIMARILY SOUTH OF I-90. THERMAL  
PROFILES AT DECORAH IN THE 24.03Z RAP KEEPING SURFACE TEMPERATURES  
RIGHT NEAR FREEZING WITH INCREASING LOW-LEVEL SATURATION FROM THE  
SURFACE TO AROUND 3KFT DURING THE EVENING, SO IF SURFACE  
TEMPERATURES TREND AT OR BELOW FREEZING CANNOT RULE OUT SOME  
LOCALIZED FREEZING DRIZZLE DURING THE EVENING AND OVERNIGHT HOURS ON  
CHRISTMAS. HOWEVER, THE JOINT PROBABILITIES FOR MEASURABLE QPF AND  
FREEZING SURFACE TEMPERATURES IN THE RECENT GRAND ENSEMBLE  
(GEFS/EC/CANADIAN ENSEMBLE) REMAIN LOW (0-20% CHANCE) DURING THE  
OVERNIGHT. OTHERWISE, TEMPERATURES FOR CHRISTMAS WILL BE SLIGHTLY  
ABOVE NORMAL IN THE BROADER UPPER-LEVEL RIDGING REGIME WITH HIGHS  
GENERALLY IN THE UPPER 20S TO UPPER 30S AREAWIDE.  
 
THURSDAY - SUNDAY: PRECIPITATION CHANCES RETURN  
 
THE UPPER-LEVEL PATTERN BEGINS TO SHIFT MORE SUBSTANTIALLY HEADING  
INTO THURSDAY WITH A SHORTWAVE TROUGH EJECTING FROM THE SOUTHERN  
ROCKIES AND INTO THE TEXAS PANHANDLE. AS THIS OCCURS, THE  
AFOREMENTIONED BROADER RIDGE WILL PUSH EASTWARD SUBJECTING OUR  
REGION TO FAIRLY ROBUST SOUTHWESTERLY FLOW. ADDITIONALLY, WARM AIR  
ADVECTION WILL NUDGE OUR TEMPERATURES FURTHER ABOVE NORMAL FROM  
THURSDAY AND INTO THE WEEKEND WITH MEDIAN HIGH TEMPERATURES IN THE  
24.00Z GRAND ENSEMBLE (GEFS/EC/CANADIAN ENSEMBLE) PUSHING HIGHS INTO  
THE 40S AREAWIDE FROM FRIDAY THROUGH SUNDAY. WITH THE AFOREMENTIONED  
PERSISTENT CLOUD COVER IN PLACE, OVERNIGHT LOW TEMPERATURES WILL NOT  
FALL MUCH WITH THE 23.12Z EFI HAVING WARM LOWS ON SATURDAY IN THE  
UPPER PERCENTILES OF MODEL CLIMATOLOGY WITH CURRENT FORECAST ONLY  
HAVING OVERNIGHT LOWS IN THE MIDDLE TO UPPER 30S.  
 
ADDITIONALLY, WITH UPPER-LEVEL SOUTHWESTERLY FLOW IN PLACE, SEVERAL  
SHORTWAVE TROUGHS MEANDER THEIR WAY NORTHBOUND TOWARDS THE REGION.  
THE FIRST OF THESE SHORTWAVES APPROACHES THE REGION FOR FRIDAY WITH  
ANY PRECIPITATION LIKELY BEING IN THE FORM OF RAIN GIVEN THE  
AFOREMENTIONED TEMPERATURES. STILL QUITE A LOT OF QUESTIONS WITH  
HOW THIS WAVE WILL AMPLIFY AND IF IT WILL GET ABSORBED INTO THE  
LARGER PARENT TROUGH TO ITS NORTHWEST. REGARDLESS, FAIRLY HIGH  
PROBABILITIES (50-80%) IN THE 24.00Z GRAND ENSEMBLE REMAIN FOR AT  
LEAST 0.1" OF QPF ACROSS THE AREA THROUGH SATURDAY MORNING WITH THE  
90TH PERCENTILE SHOWING SOME LOCALIZED AREAS OF UP TO 0.5". AS WE  
GET INTO THE WEEKEND, ADDITIONAL PRECIPITATION CHANCES REMAIN  
(20-50%) WITH THE GLOBAL DETERMINISTIC MODELS (GFS/EC/CANADIAN)  
SHOWING ADDITIONAL SHORTWAVES PIVOTING AROUND A BROADER UPPER-  
LEVEL TROUGH DRAPED ACROSS THE CENTRAL CONUS. HOWEVER, THE  
DETERMINISTIC MODELS AT THIS POINT BEGIN TO DEVIATE MORE  
SIGNIFICANTLY WITH HOW THESE SHORTWAVES PROGRESS THROUGH SO WILL  
KEEP PRECIPITATION CHANCES ON THE LOWER SIDE IN ACCORDANCE WITH  
THE NBM AT THIS MOMENT, BUT WOULD EXPECT SOME LINGERING  
PRECIPITATION THROUGH THE WEEKEND DEPENDING ON HOW THE OVERALL  
UPPER-LEVEL PATTERN RESOLVES.  
 
NEXT WEEK:  
 
AS WE MOVE TOWARDS THE NEW YEAR, GLOBAL MODELS GENERALLY AGREE ON  
MOVING THIS WEEKEND TROUGH MESS EASTWARD ALLOWING FOR ANOTHER TROUGH  
TO EJECT OUT OF THE CENTRAL ROCKIES AND MOVE THROUGH QUASI-ZONAL  
FLOW. THIS FAR OUT PREDICTABILITY IN GUIDANCE DECLINES SHARPLY.  
HOWEVER, CLUSTER ANALYSIS GENERALLY AGREES ON THE PRESENCE OF THIS  
SYSTEM FOR MONDAY/TUESDAY WITH THE INTENSITY AND EXACT POSITION  
WILL HAVE LARGE IMPLICATIONS FOR ANY LOCAL IMPACTS. REGARDLESS,  
THERE IS A FAIRLY STRONG CONSENSUS IN THE 24.00Z GRAND ENSEMBLE  
THAT TEMPERATURES WILL COOL DOWN TO BRING IN THE NEW YEAR WITH  
MEDIAN HIGH TEMPERATURES AT LA CROSSE FALLING BACK TO NEAR  
AVERAGE AT THE VERY LEAST TO START 2025.  
 
 
   
AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/  
 
ISSUED AT 1046 PM CST MON DEC 23 2024  
 
MAIN TAF CONCERNS ARE MVFR/IFR CONDITIONS AT BOTH RST/LSE TAF SITES  
THROUGH THE TAF PERIOD. WEAK LOW PRESSURE OVER THE GREAT LAKES  
REGION WILL CONTINUE TO SPREAD STRATUS DECK OF CLOUDS OVER THE  
REGION. WITH LOW LEVEL MOISTURE NEAR THE SURFACE...CEILINGS  
WILL LOWER INTO IFR AT RST TAF SITE FOR A PERIOD AFTER 10Z  
TUESDAY. WITH DAYTIME HEATING CEILINGS ARE EXPECTED TO IMPROVE  
TO MVFR AFTER 18Z TUESDAY. THEN LOWER INTO IFR CONDITIONS  
TUESDAY EVENING. SOME PATCHY FOG WILL FORM ACROSS THE AREA AS  
THE LATEST HI- RESOLUTION MODELS CONTINUE TO SUGGEST VISIBILITY  
COULD BE REDUCED TO IFR. HOWEVER CONFIDENCE IS LOW VISIBILITY  
WILL BE REDUCED TO LESS THAN 2 MILES AND WILL CONTINUE WITH A  
PERIOD OF 3 MILE VISIBILITY AT RST TAF SITE. WIND SPEEDS WILL  
REMAIN LESS THAN 10 KNOTS THROUGH THE TAF PERIOD.  
 
 
   
ARX WATCHES/WARNINGS/ADVISORIES  
 
WI...NONE.  
MN...NONE.  
IA...NONE.  
 
 
 
 
 
DISCUSSION...NAYLOR  
AVIATION...DTJ  
CLICK HERE TO GO TO PREVIOUS BULLETINS.
The Nexlab WI Page
The Nexlab IA Page
The Nexlab MN Page
Main Text Page